Stem cells are undifferentiated, or immature, cells that are capable of giving rise to multiple, specialized cell types and ultimately to terminally differentiated cells. Unlike any other cells, they are able to renew themselves such that essentially an endless supply of mature cell types can be generated when needed. Due to this capacity for self-renewal, stem cells are therapeutically useful for the regeneration and repair of tissues. Stem cells have the potential for providing benefit in a variety of clinical settings.
Embryonic stem cells are stem cells from embryos which are capable of differentiation into most, if not all, of the differentiated cell types of a mature body. Stem cells are referred to as pluripotent, which describes this capability of differentiating into many cell types. A category of pluripotent stem cell of high interest to the research community is the human embryonic stem cell, abbreviated here as human ES cell, which is an embryonic stem cell derived from a human embryonic source. Human embryonic stem cells are of great scientific interest because they are capable of indefinite proliferation in culture and are thus capable, at least in principle, of supplying cells and tissues for replacement of failing or defective human tissue. For this reason, the existence in culture of human embryonic stem cells offers the potential of unlimited amounts of human cells and tissues for use in a variety of therapeutic protocols to assist in human health. It is envisioned that human embryonic stem cells will be proliferated and directed to differentiate into specific lineages so as to develop differentiated cells or tissues which can be transplanted into human bodies for therapeutic purposes. Human embryonic stem cells and the differentiated cells that may be derived from them are also powerful scientific tools for the study of human cellular and developmental systems. However, the limitation of many of these potential applications has been obtaining a sufficient number of stem cells and stimulating terminal differentiation of these stem cells into mature tissue-specific cells.
The basic techniques used for the generation and culture of stem cells, particularly embryonic stem cells, required the use of mouse embryonic fibroblast (MEF) feeder cells as a feeder layer on which stem cells could be cultured. The fibroblast feeder cells act to encourage the stem cells to remain in an undifferentiated state. Whilst such techniques do work, there are also significant limitations and drawbacks to the procedures currently employed. For instance, there are significant concerns that one or more agents, such as a virus, could be transmitted from the feeder cells to the stem cells in culture.
Therefore, if one of the objectives of stem cell cultures is to create tissues which can ultimately be transplanted into a human body, it is highly desirable that the stem cells are never exposed to cells of another species or to cells derived from another individual. Accordingly, establishing a cell culture environment that will permit the proliferation and culture of stem cells in an undifferentiated or a substantially undifferentiated state in the absence of a feeder layer is of great interest in the continued development of techniques for the long term culture of human embryonic stem cells, as well as meeting the regulatory requirements for producing clinically acceptable stem cells, such as the generation and storage of a Master Cell Bank comprising a homogeneous population of human embryonic stem cells produced from a single cell source. Compliance with the aforementioned criteria will ensure quality assurance and safety towards maximizing clinical efficacy, the primary mandate for the Food and Drug Administration (FDA) and other such regulatory bodies. A suitable stem cell culture method that satisfies existing and future regulations under Good Tissue Practice (GTP) and Good Manufacturing Practice (GMP) will also be essential to the manufacture and use of viable material for cell based therapy. Thus, a standardized and scaleable procedure with validated and non-adventitious components is highly advantageous.
The present invention overcomes, or at least alleviates, some of the aforementioned problems of the art by providing a method of culturing a stem cell in the absence of feeder cells and preferably without relying on an ECM (or a similar growth matrix) culture platform.
The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.